(CNN) Space needs cleaning if costly catastrophic collisions are to be avoided, scientists warn.
Several litter-picking ideas to remove space junk from Earth orbit, including a net, a harpoon and a sail are due to be tested later in 2017.
Led by scientists from the Surrey Space Centre in the UK and funded by the European Commission, the RemoveDEBRIS project aims to tackle the growing problem of orbiting garbage that threatens satellites vital for the Internet, cell phones and navigation.
Space exploration 'at risk'
The group estimates that there is more than 7,000 tons of junk in circulation and NASA says more than 20,000 of the larger pieces are being tracked.
Debris ranges in size from large chunks of dead satellites and used rockets to flecks of paint. They are moving so fast -- faster than a bullet -- that even strikes from small fragments could be disastrous.
A chip in a window on the International Space Station (ISS) was recently photographed by visiting European Space Agency (ESA) astronaut Tim Peake. It is thought to have been caused by a paint flake or a miniscule metal fragment.
RemoveDEBRIS lead scientist Jason Forshaw told CNN: "We are reaching a situation where there's a huge amount of junk in space. People say space is big, but the reality is that the junk is contained in orbits that are commonly used."
The RemoveDEBRIS mission aims to tests a net for catching rogue satellites.
He warned that missions costing hundreds of millions of dollars are at risk, with a real chance of satellites being "wiped out."
READ: Space harpoon to nail orbital garbage
In partnership with Airbus and several others, the $15.7 million mission aims to release a small cube to test a variety of tools to grab the junk.
Once captured, debris be dragged back into the atmosphere where it would burn up. Another system uses a harpoon and what the team calls a "dragsail" that could be attached to larger pieces.
Cassini mission to end in fiery death
As one mission begins, another is coming to an end in 2017 as the Saturn probe Cassini is prepared for the final phase of its 20-year odyssey.
Launched in 1997, it has been sending data from the gas giant since 2004 but is now running low on fuel and when it runs out operators will not be able to control the spacecraft.
NASA and its mission partners from 17 countries want to prevent a possible collision and contamination of Saturn's moons Enceladus and Titan. They have chosen to send Cassini to a fiery death in Saturn's atmosphere.
But in what NASA is calling a "grand finale," Cassini will leap over Saturn's rings and make a "final series of daring dives between the planet and the inner edge of the rings."
Cassini's primary mission was to last four years but has been extended twice. NASA says on the project website that the spacecraft will collect "incredibly rich" information in its last act that the original planners might never have imagined.
Cassini will make detailed maps of Saturn's gravity and magnetic fields, sample icy ring particles and take ultra-close images of the planet's rings and clouds.
"What we learn from these activities will help to improve our understanding of how giant planets -- and families of planets everywhere -- form and evolve," NASA says on its website.
The final days of the Cassini mission may help with ongoing analysis of exoplanets -- planets beyond our solar system -- and two missions are planned to search for more of these alien worlds with launches in late 2017 or 2018.
In search of other worlds
Weird and wonderful planets beyond our solar system
An artists's conception shows planet LP 791-18d. The volcanically active planet, which is a similar size to Earth, was discovered by NASA's Spitzer Space Telescope.
This artist's illustration depicts the rocky exoplanet GJ 486 b, which orbits a red dwarf star located 26 light-years away from Earth. Astronomers have detected hints of water vapor in the system, but they can't be sure if it signifies a planetary atmosphere or if it's part of the star.
This illustration shows an Earth-size exoplanet called TOI 700 e, discovered orbiting the small, cool M dwarf star TOI 700, which is located 100 light-years away. Its other Earth-size sibling, TOI 700 d, can be seen in the distance.
TOI 700 d is the first potentially habitable Earth-size planet spotted by NASA's planet-hunting TESS mission.
Artist's impression of the exoplanet WASP-121 b. It belongs to the class of hot Jupiters. Due to its proximity to the central star, the planet's rotation is tidally locked to its orbit around it. As a result, one of WASP-121 b's hemispheres always faces the star, heating it to temperatures of up to 3000 degrees Celsius. The night side is always oriented towards cold space, which is why it is 1500 degrees Celsius cooler there.
This artist's impression shows a close-up view of Proxima d, a planet candidate recently found orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. The planet is believed to be rocky and to have a mass about a quarter that of Earth. Two other planets known to orbit Proxima Centauri are visible in the image too: Proxima b, a planet with about the same mass as Earth that orbits the star every 11 days and is within the habitable zone, and candidate Proxima c, which is on a longer five-year orbit around the star.
The discovery of a second exomoon candidate hints at the possibility that exomoons may be as common as exoplanets.
This artist's impression shows the football-shaped planet WASP-103b (left) closely orbiting its host star.
This image shows double-star system b Centauri and its giant planet b Centauri b. The star pair is the bright object at top left. The planet is visible as a bright dot in the lower right. The other bright dot (top right) is a background star.
This artist's rendering shows a Jupiter-like planet orbiting a dead white dwarf star 6,500 light-years away from Earth. The planet survived the violent phases of stellar evolution leading to the star's death.
This artist's illustration shows the night-side view of the exoplanet WASP-76b, where iron rains down from the sky.
Astronomers have identified a new class of habitable planets, which they call Hycean planets. These are hot, ocean-covered planets with hydrogen-rich atmospheres.
This artist's illustration shows L 98-59b, one of the planets in a planetary system 35 light-years away from Earth. This planet has half the mass of Venus.
In this artist's illustration, two gaseous exoplanets can be seen orbiting the bright sun-like star HD 152843.
An artist's rendering of TOI-1231 b, a Neptune-like planet about 90 light years away from Earth.
This artist's conception depicts a violent flare erupting on the star Proxima Centauri as seen from the viewpoint of a planet orbiting the star called Proxima Centauri b.
After losing its gaseous envelope, the Earth-size core of an exoplanet formed a second atmosphere. It's a toxic blend of hydrogen, methane, and hydrogen cyanide that is likely fueled by volcanic activity occurring beneath a thin crust, leading to its cracked appearance.
This illustration shows the metaphorical measuring of the density of each of the seven planets in the nearby TRAPPIST-1 system. New measurements have revealed the most precise densities yet for these planets and they're very similar -- which means they also likely have similar compositions.
This artist's illustration shows the view from the furthest planet in the TOI-178 system.
This artist's illustration shows TOI-561b, one of the oldest and most metal-poor planetary systems discovered yet in the Milky Way galaxy. Astronomers found a super-Earth and two other planets orbiting the star.
This massive and distant exoplanet, called HD106906 b, has an elongated and angled orbit that causes it to take 15,000 Earth years to complete one lap around its twin stars.
This is an artist's impression of a free-floating rogue planet being detected in our Milky Way galaxy using a technique called microlensing. Microlensing occurs when an object in space can warp space-time.
This is an artist's impression of exoplanet WASP-189 b orbiting its host star. The star appears to glow blue because it's more than 2,000 degrees hotter than our sun. The planet, which is slightly larger than Jupiter, has a tilted orbit around the star's poles rather than its equator.
For the first time, an exoplanet has been found orbiting a dead star known as a white dwarf. In this artist's illustration, the Jupiter-sized planet WD 1856 b orbits the white dwarf every day and a half.
This illustration shows a carbon-rich planet with diamond and silica as ts main minerals. Water can convert a carbon-rich planet into one that's made of diamonds. In the interior, the main minerals would be diamond and silica (a layer with crystals in the illustration). The core (dark blue) might be made of an iron-carbon alloy.
This image shows a young sun-like star being orbited by two gas giant exoplanets. It was taken by the SPHERE instrument on European Southern Observatory's Very Large Telescope. The star can be seen in the top left corner, and the planets are the two bright dots.
This artist's impression shows a Neptune-sized planet in the Neptunian Desert. It is extremely rare to find an object of this size and density so close to its star.
This is an artist's impression of the multiplanetary system of newly discovered super-Earths orbiting a nearby red dwarf star called Gliese 887.
The newly discovered exoplanet AU Mic b is about the size of Neptune.
This artist's impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. Proxima b is a little more massive than the Earth.
This is an artist's illustration of an exoplanet's atmosphere with a white dwarf star visible on the horizon. The starlight of a white dwarf filtered through the atmosphere of an exoplanet that's orbiting it could reveal if the planet has biosignatures.
This is an artist's illustration of the Kepler-88 planetary system, where one giant exoplanet and two smaller planets orbit the Kepler-88 star. The system is more than 1,200 light-years away.
ESA's CHEOPS space telescope will study in detail the bright stars already known to host planets with the aim of measuring the density of what it calls "super-Earths" and gas giant planets.
It is hoped that the mission will find likely targets for further study.
Thousands of children across Europe took part in a competition to submit drawings that will be sent into space on board the satellite. A total of 3,000 were selected and will be shrunk and engraved on two metal plaques.
In collaboration with SpaceX and other contractors, NASA is also planning an exoplanet mission.
TESS -- or Transiting Exoplanet Survey Satellite -- is designed to detect small planets that might be orbiting nearby stars.
NASA says that during its two-year mission it will monitor the light from more than 200,000 stars, searching for temporary dips in brightness as planets pass between Earth and the target star.
Scientists say the craft is expected to catalog more than 1,500 exoplanet candidates including 500 of a comparable size to the Earth.
NASA lists the working launch date as December 2017.
Focus on reusable spacecraft
This year may also see more testing in the space race between private companies SpaceX founded by Elon Musk, the product architect of Tesla; Blue Origin, set up by Amazon founder Jeff Bezos; and Virgin Galactic led by British entrepreneur Richard Branson.
All three are vying to make space travel cheaper, focusing on landing and reusing spacecraft.
SpaceX is developing the Dragon 2 spacecraft designed to carry cargo and ferry astronauts into space. It has been selected by NASA as one of the candidates to take them to the ISS. The company says on its website that manned flights will take place in "2-3 years."
NASA has also awarded a contract to Blue Origin to supply reusable launch vehicles -- joining five other companies developing new craft.
Blue Origin President Rob Meyerson told reporters at a space symposium in October that the company was "still on track for flying people -- our test astronauts -- by the end of 2017." Blue Origin told CNN it has nothing to add to that at this time.
Lockheed and NASA spent 2016 fitting avionics and propulsion tubing to their Orion spacecraft. And in the spring of 2017 they plan to turn on the computers as well as fit the heat shield and ESA's service module. An Orion manned flight planned for 2021 will take astronauts around the Moon.
China aims for the Moon first
China continues to push its own ambitious space program -- and may reach a major milestone in 2017.
China's National Space Administration has already said it will target a landing on the dark side of the Moon by 2018 and reach Mars by the end of 2020.
But deputy chief of the space program, Wu Yanhua, also confirmed last month that it will launch the Chang'e-5 lunar probe by the end of 2017, returning a Moon sample to Earth in the process.